To study extracellular matrix vesicles which appear to play an initiating role in calcification of cartilage, bone and dentin. These sub-microscopic, extracellular membranous vesicles were first identified and described in the matrix of calcifying cartilage. Subsequently, we isolated matrix vesicles from normal and rachitic growth cartilage and demonstrated that they contain much phosphatase, especially alkaline phosphatase, ATPase and inorganic PPiase, and are enriched in lipids, especially acidic phospholipids. All of these enzymes and lipids have been implicated in the calcification mechanism. Two major questions require further study: 1) the mechanism of vesicles calcification and 2) the mode of biogenesis of matrix vesicles. We intend to study vesicle calcification in rachitic cartilage and embryonic bone. Procedures have been worked out for culture and assay of calcium uptake by both of these tissues. Controlling factors in vesicle calcification will be identified by altering culture conditions, and then tested for their ability to stimulate or inhibit calcium uptake by isolated matrix vesicles. We shall also attempt to further characterize matrix vesicle phosphatases. In order to study the biogenesis of matrix vesicles, we propose using autoradiography coupled with electron microscopy to observe uptake into precursor cells and release into the matrix of membrane lipid precursor (such as 3H-glycerol). BIBLIOGRAPHIC REFERENCES: Anderson, H.C. Introduction to the First International Conference on Matrix Vesicle Calcification. Fed. Proc. 35:105-108, 1976. Anderson, H.C. and Sajdera, S.W. Calcification of rachitic cartilage to study matrix vesicle function. Fed. Proc. 35: 148-152, 1976.